Transportation Deployment Casebook/Trolleybus

Trolleybuses are electrically powered buses. Unlike other electric vehicles, however, trolleybuses draw their power from overhead lines running along the trolleybus’ route instead of batteries. The bus is connected to the line by two poles and wires, whereas a conventional trolley draws its electricity from a single connection point overhead.[1] While there are limitations in route choice due to the vehicle requiring a tie-in to the line at all times during operation, this method of drawing power does provide advantages over traditional electric vehicles (as well as non-electric).

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The trolleybus dates back to 1882 in Berlin, in its origins as “Elektromode”. The Elektromote was run on a 591 yard track between train stations. It consisted of a four-wheel carriage equipped with motors run off electricity from an overhead cable. The track was dismantled after a few months of demonstration.[2]

The first “true” passenger-carrying trolleybus was developed and implemented nearly 20 years later, in Fontainebleau, near Paris, which ran until 1913.[3] Later in 1901, a system opened in Biela Valley, near Dresden, Germany. This trolleybus, like its modern counterpart, used two overhead wires with spring-loaded connection poles to draw power. This system ran until 1904, inspiring other systems around the world.[4] In 1903, trolleybuses were introduced to the United States in a demonstration in New Haven, Connecticut, and Scranton, Pennsylvania. By the 1920s many systems around the country were up and running, and the number only increased over the next 30 years. In the mode’s peak years, near and just after 1950, over 900 trolleybus systems were operating worldwide.[5]

However, due to the advent of the private vehicle and diesel bus, as well as the Federal Aid Highway act of 1956, the trolleybus fell into rapid decline along with other form of mass transit, like the streetcar.[6] The trolleybus reached maturity and did not stay there long. By 1951 and 1952, there were over 7000 trolleybus vehicles in operation. By 1956, that number had decreased to just under 6000. By 1973, the number was down to just over 700, a tenth of what it had been twenty years prior.[7]

By 2010, only around 570 trolleybus vehicles were operational in 5 states: California (San Francisco), Massachusettes (Boston), Ohio (Dayton), Pennsylvania (Philadelphia), and Washington (Seattle).[5] Just as the traditional streetcar has seen a revival by city planners, it is possible that trolleybuses will regain popularity. In some countries, like Russia, the trolleybus never experienced a decline. The system in Moscow has around 1500 vehicles and 100 lines.[8] However, as more US cities are exploring the possibility of implementing trolleybuses again, cities with existing systems like Seattle are looking at reducing or eliminating the service completely. By 2013, all of Seattle’s electric bus fleet will need replacing; in 2011 a comprehensive trolleybus system evaluation was held to determine whether or not the trolleybuses would be replaced by diesel.[9]

Trolleybuses are able to accelerate faster, more smoothly, and more effectively up hills than their non-electric counterparts. Electric motors are more effective than diesel when providing torque upon startup. In addition, their rubber tires have better traction than steel wheels on steel rails. This may be why San Francisco and Seattle, both hilly cities, still use trolleybuses today when most American cities have switched away from the mode. Trolleybuses are lighter than their counterparts as well, due to not having a standalone battery carrying the charge required for operation.[10]

Another advantage is that while the trolleybus runs on a fixed route, disabled vehicles can easily be detached from the overhead line and moved out of the way, rather than impeding other vehicles upon the same route. In addition, this allows trolleybuses to pull up to the curb as other buses do instead of requiring boarding islands in the middle of the street. This also promotes level-boarding, making accessibility to the mode easier to pedestrians with mobility impairments than those modes which cannot provide level boarding.[4]

Something that may be both an advantage and disadvantage to the technology is its quietness in operation. Pedestrians may not notice a vehicle coming when it does not make noise. To combat injuries and accidents due to this, speakers may be attached to the front of the vehicles which may direct sound toward pedestrians and other motorists in danger areas.[10]

A disadvantage is that while a trolleybus is more maneuverable than a fixed-track method of transit (LRT, streetcar) it is less so than a bus. If a road is undergoing construction in an area the trolleybus line runs, the line has to be discontinued temporarily, rather than re-routed. Also, trolleybuses cannot overtake one another like modes of non-fixed track transit can.

An overhead, three way trolleybus switch

Another major disadvantage to the trolleybus system is the need for overhead cables. The cables are considered by most to be visually unattractive, and installation of new lines may be cause for protest. Where lines come together, the effect can be especially hard to ignore. In addition to being unsightly, the cable connectors can come undone or be actively disconnected. This will cause delays in transit while the driver must reconnect the cable. Also to be considered is the effect of weather on the cables and the cable-poles; if installed in a wet and cold climate, the wires may ice up, causing the line to be unusable.

Like with non-cable buses, another point to consider is the wear and tear to the roadway by sustained heavy vehicle impact. Rail transit has an advantage here, as once the rail tracks are put in place, excessive loading is removed from the pavement. Another comparison to non-cable buses is that travel by bus is deemed less pleasant than other modes of transit. Cleanliness, demographics, and schedule reliability are potential reasons why people choose not to take a form of bus when other modes are available.

Environmental impacts of the trolleybus are also an advantage to using this mode. Any sort of mass transit has an advantage over the personal vehicle, using less energy and space. Installing a trolleybus service is more initially expensive than establishing diesel-powered bus routes due to the cost of installing overhead lines, but that extra cost may be recoverable due to lower fuel and maintenance costs. In addition, cities that draw large amounts of power from sustainable sources and use that power to operate a trolleybus system are much more sustainable than not; Seattle, Washington, USA uses hydroelectric power from the Columbia and other rivers to operate the system.[9]

Streetcars and other forms of rail transit are seeing rebirth in many cities (such as the LRT lines in Minnesota). It is possible that trolleybuses will see rebirth, as well; a more likely renaissance will come from hybrid technologies. Hybrid trolleybuses allow for a majority of the line to be placed under cable, but with an option for a battery or diesel-powered engine to cover distances where putting cable in is unfeasible, or in the event of the need for rerouting. This still may result in issues; adding batteries or engines to the vehicle will increase the cost of production as well as increasing the vehicle's weight, and giving up space for passengers.

Although trolleybuses may not see a rebirth, a related technology—trolleytrucks—are being proposed as a supplement to cargo trains. Trolleytrucks operate under the same principle as trolleybuses, and are powered by connecting to overhead wires. In the 2008 book, Transport Revolutions, authors Richard Gilbert and Anthony Perl propose a plan that would move a majority of cargo shipments from trucks onto trolleytrucks.[11] Currently, Los Angeles is looking at implementing hybrid-diesel-trolleytrucks in an effort to combat air pollution due to the shipping industry.[12]

Data were taken from the APTA 2012 Public Transportation Fact Book, found online. The oldest data presented by APTA comes from 1928, approximately 25 years after the first trolleybus systems were established in the United States. Data is continuous until 2010. This dataset is unique in that the entirety of the innovation period of the trolleybus in the United States was completed roughly 30 years after its initiation, around 1952.[7]

The innovation of a new technology (transportation or not) can be described as an S-curve with four major parts: birth, growth, maturity and decline. Initially after a technology is developed, its growth is slow as people are hesitant to adapt to it. Once it reaches a certain level (perhaps of understanding and/or acceptance), the growth exponentially increases. At another certain level, this growth slows and remains steady (possibly due to physical constraints, e.g. miles of land available for building interstate, number of cell phones the population can reasonably own). As the technology ages and newer technology develops, the old will decline, sometimes rapidly and sometimes slowly.

In the trolleybus life cycle graph, the entirety of the life cycle is shown; one can see the clear S-curve innovation period of birth, growth and maturity followed by a drastic decline.

Graph 2: Trolleybus real data v. statistical model

In order to perform statistical modeling, only the innovation period (1928–1952) was analyzed. An Ordinary Least Squares (logistic) regression model was applied to estimate the following logistic function:

S(t) = K/[1+exp(-b(t-t0)]

Where:

S(t) is the status measure (number of vehicles)

t is time (annual, 1928–1952)

(t0 is the inflection time (half of the peak)

K is saturation status level (the peak)

And b is a coefficient, measuring an amount of impact on the independent variable.

As the life-cycle of the trolleybus has already run through a complete iteration, K could be set to the peak value (7180 vehicles, in 1952) and t0 could be estimated as the year in which half that number of vehicles was reached (roughly 3590, in 1944). Using Solver, multiple iterations of analysis were run and final values of K=7951 and b= 0.225 were achieved. The resulting equation is then: